Both the stopwatch and GPS would indicate ground speed, what you were lacking is air speed. On a windy day like today was here that can make quite a difference.
Can't be sure but I think I would have made it back but without declaring anything. There would be more parameters, though, like "how well do I know the terrain between here and my home field" and "what facilities are available for setting the ASI right". No use turning back to a grass strip with no facilities whatsoever.
Only this morning I heard someone just after departure calling "coming back to the field for minor technical issue" or words to that effect.
The main point, though, is this: you got into a certain degree of problems, and got home successfully. Well done!